What stabilizer does
Cyanuric acid (CYA), sold as stabilizer or conditioner, protects chlorine from sunlight. Without it, the sun can destroy most of the free chlorine in an outdoor pool within a few hours. CYA works by binding chlorine loosely and releasing it as needed. The trade-off is that bound chlorine kills germs more slowly, so the more CYA you have, the higher your free chlorine has to be.
The Oregon Health Authority, which follows the CDC’s code for public pools, gives 30 to 50 ppm as the ideal range. The CDC’s Model Aquatic Health Code caps public pools at 90 ppm. Indoor pools don’t get sunlight, so they gain nothing from CYA, and the CDC advises against it in hot tubs.
The formula
Cyanuric acid (g) = CYA rise (ppm) × litres ÷ 1,000 ÷ purity
Granular stabilizer is close to pure cyanuric acid. Liquid stabilizers are weaker and list their strength on the label. 13 oz per 10,000 gallons raises CYA by 10 ppm.Worked example
15,000 gallons, CYA 10 to 40 ppm, granular stabilizer
- Rise = 30 ppm
- Stabilizer = 30 × 56,781 L ÷ 1,000 ÷ 0.99 = 1,721 g = 3.79 lb
- At 40 ppm CYA, keep free chlorine near 5 ppm and never below 3
How CYA changes your chlorine target
Free chlorine to hold as CYA rises
This is why high CYA is a problem. At 100 ppm CYA you need about 12 ppm of free chlorine for the same protection that 5 ppm gives at 40 ppm, and a shock to clear algae needs around 39 ppm.
How to add stabilizer
- Granular CYA dissolves slowly. Put it in a sock or mesh bag in the skimmer basket, or dissolve it in a bucket of warm water and pour that in front of a return jet.
- Don’t backwash or clean the filter for about a week, or you’ll throw away undissolved stabilizer.
- Wait 7 days, then retest before adding more. CYA tests are imprecise, so look for a clear change.
- Trichlor tablets and dichlor add CYA every time you use them, about 0.6 ppm and 0.9 ppm of CYA for every 1 ppm of chlorine. If you chlorinate with them, you may never need to add stabilizer separately.
How to lower stabilizer
CYA doesn’t evaporate, break down in normal pool conditions, or get used up by chlorine. The reliable fix is to replace some water. To go from 100 to 50 ppm you would drain and refill 50% of the pool. The drain and refill calculator works it out, including partial drains.
Frequently asked questions
How much stabilizer do I add to my pool?
About 13 oz of granular cyanuric acid per 10,000 gallons for each 10 ppm you want to raise it. To go from 0 to 40 ppm in 10,000 gallons, that’s about 3.34 lb.
What should my CYA level be?
For an outdoor pool chlorinated with liquid chlorine, 30 to 50 ppm is the usual range. Some salt-cell makers recommend higher; follow your manual. Public pools are capped at 90 ppm.
Is stabilizer the same as conditioner and cyanuric acid?
Yes. Stabilizer, conditioner and CYA are all names for cyanuric acid.
How long does stabilizer take to dissolve?
Granular CYA can take several days to dissolve fully and register on a test. Retest after about a week.
How do I lower cyanuric acid in my pool?
Drain part of the water and refill with fresh water. Some products claim to break CYA down biologically, with mixed results.
Should I use stabilizer in an indoor pool or hot tub?
Usually not. Indoors there’s no sunlight to protect against, so CYA only slows chlorine down. The CDC advises against CYA in hot tubs.
Sources
- Cyanuric Acid (fact sheet 6). Oregon Health Authority.
- Model Aquatic Health Code, 5th edition (2024). CDC.
- Home Pool and Hot Tub Water Treatment and Testing. U.S. Centers for Disease Control and Prevention (CDC), reviewed May 10, 2024.
- Understanding the Chlorine/CYA Chart. Trouble Free Pool.
- What increases cyanuric acid (CYA) in a swimming pool?. Orenda Technologies.
Reviewed November 7, 2026. We check the formulas against the sources above and re-run the worked examples whenever we update this page. Found something wrong? Tell us.